Influenza and Other Respiratory Diseases in Southern Hemisphere The NCIRD Influenza Division (ID) is cooperating with the WHO Collaborating Center for Studies on the Ecology of Influenza in Animals and Birds, and with New Zealand public health laboratories and Universities to conduct a five year study in the southern hemisphere on influenza and other respiratory diseases; their burden, epidemiology, transmission, risk factors, and the effectiveness of vaccination. The influenza season in New Zealand occurs during the northern hemisphere summer, and therefore can provide critical information on the epidemiology, burden, strains and effectiveness of prevention measures of influenza and other respiratory pathogens at a time when study sites in the northern hemisphere cannot. In addition, understanding the epidemiology of influenza and the effectiveness of annual vaccines in the southern hemisphere will provide needed data for influenza control strategies in other parts of the world. The first primary objective of the study is to estimate and assess the incidence rate, prevalence and clinical spectrum, pathogenesis and outcomes of severe pneumonia and severe acute respiratory infection (SARI) caused by types and subtypes of influenza viruses and other respiratory pathogens and differences of these parameters among population sub-groups at possibly increased risk for disease. The second primary objective is to assess the annual effectiveness of influenza vaccines in preventing laboratory confirmed influenza, through observational studies of existing programs including differential effectiveness among subpopulations. In addition to the primary objectives, additional studies to be conducted on interaction between influenza infection and other infections, etiologies and causes of respiratory mortality, non-severe illness due to influenza and other respiratory pathogens, serological studies of annual infection risk, impact of various risk factors for influenza infection or severe disease, immune response to influenza, healthcare and societal economic burden of influenza disease, and assessment of cost-effectiveness of influenza vaccination. These assessments will be made for the Auckland population in New Zealand through the establishment of enhanced real-time surveillance in sentinel practices and hospitals.